Eliminating humming & buzzing

What is the best way to have a clean sound? When I hook
up the grounding connector from my turntable, it reduces
about 95% of the humming/buzzing; but not all of it. The
noise is still there even if I unplug the power from the
table.

Is this simply a grounding problem, or is there something
more that I need to do? The table is hooked up to a
receiver which is not at all grounded; I just connect the
table ground to the ground in my power strip. Kind of
primitive, I realize, which is why I'm asking here.

Thanks!
Mark